LO2: Volcanoes

Composite / strato volcano

• Forming along convergent plate boundaries

• Tall, steep sided and cone shaped, reaching several thousand meters

• Built from alternating layers of lava and as

• Andesitic magma (viscous with high gas content)

Shield volcano

• Forming along divergent plate boundaries + hot spots

• Low, gently sloped domes with wide bases

• Built from lava, erupting from fissures and the crater

• Basaltic magma (runny with low gas content)

How are strato volcanoes formed?

1. Mantle is heated so it is less dense and will rise

2. Mantle drags plates towards each other by friction

3. Oceanic plate subducts under the continental plate

4. The oceanic plate melts because of friction causing heat and the hot mantle

5. Hot melted plate rises through the continental plate creating a magma chamber for the volcano to form on.

Ocean trenches form in gap between oceanic and continental plate, and so do deep strong earthquakes

Where are strato volcanoes regularly near?

Near oceans because of the oceanic plate

Andesitic magma?

• High content of silica making it more viscous

• High value of dissolved gases causing explosive eruptions

Constructive plate boundary

1. Uplifting mantle drags the two oceanic plates apart

2. Some of the hot mantle rises through fissures and the gap between the two plates

3. Volcano builds up over repeated eruptions releasing lava

Basaltic lava?

• Low silica content making it runny

• Low gas content so there are less explosive eruptions.

Andesitic Lava (strato)

• Higher silica content

• More viscous (sticky and thick)

• Flows slower and less far

• Higher gas concentration

• More explosive and violent (volcanic bombs)

• Less frequent eruptions

Basaltic Lava (shield)

• Less silica content

• Less viscous (runny)

• Flows faster and further before cooling

• Lower gas concentration

• Less explosive and violent (lives rarely lost + crops often destroyed)

• More frequent (potentially continuous) eruptions

What are volcanic hotspots?

Where volcanoes form away from the plate boundaries

When a superheated plume of rock slowly rises through the mantle

After reaching the upper mantle, it melts the asthenosphere and base of the lithosphere

Magma rises through weaknesses in the crust, erupting along the Earth’s surface

Eg. Hawaii (oceanic, shield), Yellowstone (continental, strato / super)

Why are the youngest volcanoes above the hot spot?

The oldest is further away from the hotspot because the direction of plate movement is away from the hotspot.

Younger volcanoes at hotspots are…

Larger because newly constructed

Older volcanoes at hotspots are….

Smaller becoming sea mounts due to erosion.

Primary Hazard

Immediate damage

Emergency Response

Immediate response

Secondary Hazard

Knock - on effect

Long-term respone

Putting area back to normal and future preparation

Volcanologist

Someone who works with volcanoes who can monitor them and reduce risks

Tiltmeter / satellite

Ballooning and bulging in the ground, and increase in ground bulging means more likely to erupt

Seismograph / seismometer

Checks for seismic activity such as tremous, and increase in tremours means more likely to erupt

Gas Monitoring

Checking for degassing such as SO2 production, increase in amount of degassing means more likely to erupt

Thermal imaging

Ground temperatures near volcanoes, an increase in temperatures means more likely to erupt